The present invention relates to a biosensor for facilitating rapid and highly accurate quantification of a substrate such as glucose contained in a sample.
With the aim of realizing simple quantification of body fluid components by ordinary people, various types of biosensors have recently been developed which utilize a specific catalytic action of enzymes.
In the following, a method of glucose quantification will be explained as an example of the method of quantifying a component contained in a sample solution. As an electrochemical method of glucose quantification, a method using a combination of glucose oxidase (hereinafter abbreviated to GOD) with an oxygen electrode or a hydrogen peroxide electrode is generally well-known.
GOD selectively oxidizes xcex2-D-glucose as a substrate to D-glucono-xcex4-lactone using oxygen as an electron mediator. In the presence of oxygen, oxygen is reduced to hydrogen peroxide during the oxidation reaction process by GOD. The decreased volume of oxygen is measured by the oxygen electrode, or the increased volume of hydrogen peroxide is measured by the hydrogen peroxide electrode. The decreased volume of oxygen and the increased volume of hydrogen peroxide are proportional to the content of glucose in the sample solution, so that the quantification of glucose is possible based on the decreased volume of oxygen or the increased volume of hydrogen peroxide.
Glucose sensors of new type have been developed which use as the electron mediator an organic compound or a metal complex such as potassium ferricyanide, a ferrocene derivative and a quinone derivative without using oxygen as the electron mediator. The sensors of this type oxidize the reductant of electron mediator resulting from the enzyme reaction on an electrode, whereby the concentration of glucose contained in the sample solution can be determined based on the amount of the oxidation current. In the case of using such an organic compound or metal complex as the electron mediator in place of oxygen, it is possible to form a reagent layer while the electron mediator is carried in a precise amount and in a stable state together with GOD on the electrode. Further, it is also possible to integrate the reagent layer with an electrode system while keeping it in an almost dry state. Disposable glucose sensors developed based on these technologies have recently been receiving a lot of attention. A typical example thereof is a biosensor disclosed in Japanese Patent Publication No. 2517153. In such a disposable glucose sensor, it is possible to measure the glucose concentration easily with a measurement device by simply introducing the sample solution into the sensor connected detachably to the measurement device.
In the measuring method using the above-described glucose sensor, by a response current of 1 to 10 xcexcA/cm2 order, the glucose concentration in the sample can be measured in about 30 seconds. However, it is desired from various fields to develop sensors capable of more rapid glucose quantification with higher sensitivity and accuracy in recent years.
Also, in conventional electrochemical glucose sensors, by the addition of a hydrophilic polymer such as carboxymethyl cellulose to the reagent layer, the measurement results are prevented from being affected by vibrations given to the measurement device from outside. The hydrophilic polymer has another merit that it can function as a binder to immobilize the enzyme on the electrode moderately. The presence of the hydrophilic polymer, however, causes changes in catalytic activity of GOD or thermodynamics of the hydrolytic reaction from D-glucono-xcex4-lactone to gluconic acid, thereby to cause accumulation of D-glucono-xcex4-lactone, which is a product of the GOD reaction, in some cases. As a result, the reverse reaction proceeds and the rate of the glucose oxidation reaction decreases, thereby to lower the amount of the reductant of electron mediator generated in a short reaction time, so that the magnitude (sensitivity) of the current of the sensor flowing in response to glucose decreases in some cases. Particularly, trying to obtain a sufficient sensitivity to high concentrations of glucose while securing a good accuracy requires an increase in reaction time in order to generate a large amount of the reductant of electron mediator, so that the measurement tends to require longer time.
The present invention relates to a biosensor comprising an electrically insulating base plate, an electrode system containing a working electrode and a counter electrode disposed on the base plate, and a reagent system comprising at least an oxidoreductase, a hydrophilic polymer and an electron mediator, wherein the reagent system further comprises a substance having a function to convert an organic product generated by direct reaction of a substrate to be measured with the oxidoreductase to another compound.
The present invention provides a biosensor comprising an electrically insulating base plate, an electrode system containing a working electrode and a counter electrode disposed on the base plate, a cover member disposed over the base plate to form a sample solution supply pathway to the electrode system between the cover member and the base plate, and a reagent system provided to a portion exposed to the sample solution supply pathway, wherein the reagent system comprises at least an oxidoreductase, a hydrophilic polymer, an electron mediator, and a substance having a function to convert an organic product generated by direct reaction of a substrate to be measured with the oxidoreductase to another compound.